Informed consent are being sought from patients with epilepsy that metabolize AEDs at a slow rate (Group 1), at an average rate (Grou( 2), and family members of the slow metabolizers (Group 3). Patients (Group 1), controls (Group 2), and family members (Group 3) will be brought to steady state with the AED that they normally take (Groups 1 and 2) or with a low dose of the AED that their family member from Group 1 is taking (Group 3). Participants will be asked to report to the CRC at the University of MN where they will be admitted for approximately 24 hours. The same dosage regimen (q12) will be continued throughout the patients' stay at the CRC. A small indwelling catheter will be inserted into a vein in the patient's forearm so that multiple blood samples can be conveniently taken. Patients will be asked to collect their urine into a container over a 24 hour period beginning just prior to the taking of the blood sample. Blood and urine specimens will be analyzed for blood chemistries (to assess liver function, kidney function, and the amount of protein binding) for creatinine clearance (to assess kidney function) and for the parent drug and metabolite concentrations (to assess the contribution of specific metabolic pathways to AED metabolism).